Scripture for Ashwini Mudra

Question

In which scripture Ashwini mudra is mentioned?

Ashwini mudra is a beginner yoga technique that involves contracting the anal sphincter in a rhythmic way in order to direct prana (life force energy) upward along the spine through the sushumna nadi, or the body's main energy channel. The name, ashwini mudra, comes from the Sanskrit, ashwa, meaning “horse,” and mudra, which means “gesture” or “sign.”

Ashwini mudra is often practiced in a comfortable seated posture such as padmasana (lotus pose), siddhasana(accomplished pose), sukhasana (easy pose) or vajrasana (thunderbolt pose)

Answer 1

You can find it being mentioned in the Gheranda SamhitA. The above pic is taken from this PDF of the text.

In Chapter 3 of the text several MudrAs are described. In that list, the 21st MudrA is the Aswini MudrA.

You can check page 38 of the PDF. The verses describing the MudrA and it's benefits are respectively the 82nd and 83rd verses of Chapter 3 (given below).

Aswnini paramA mudrA guhya roga vinAshini |
Bala pushtikAri chaiva akAla maranam hareth ||

This Aswini is a great MudrA; it destroys all diseases of the rectum; it gives strength vigour, and prevents preamture death.

Akunchayet gudadwAram prakAshayet punah punah |
SA saveda aswini mudrA shakti pravodha kArini ||

Contract and dilate the anal aperture again and again, this is called Aswini MudrA. It awakens the Shakti (Kundalini).